I cannot find out for sure if the oil that I'm using is synthetic or mineral. I have suspicions that it is mineral based on unreliable web sites, but the recommended oil for my car (Renault Megane MK1 1.6e 1998) is synthetic. How can I check which one it is? And does it matter?

2 Answers
2

Based on this link, I would say that you are dealing with a mineral oil:

Premium quality mineral based engine oil, delivers excellent engine
cleanliness and protection against wear and corrosion under a wide
under a wide variety of operating conditions for cars and vans with
gasoline and diesel engines.

With respect to whether it really matters, the short answer is "it depends but probably not enough for you to notice." To say more than that, we'd have to know much more about the specific vehicle, the maintenance history and its usage profile.

Yes you can mix synthetic with other oils. Your manufacturer usually just specifies a certain specification or certification that the oil must meet. As long as the oil meets the spec it will perform fine, regardless whether it is synthetic or mineral.